- SIGSTOP/SIGTSTP/SIGTTIN/SIGTTOU stop, SIGCONT resumes; the parent gets
SIGCHLD and wait4 reports WUNTRACED/WCONTINUED; ps shows T. Ctrl-Z works,
and mc no longer hangs waiting for its subshell to stop.
- Blocking reads (console, pty, pipe) and sleeps take a pending stop and
carry on after SIGCONT; a caught signal without SA_RESTART ends them
with EINTR.
- nanosleep reads tv_nsec (sleep 0.5 used to return at once), writes the
remainder, and clock_nanosleep understands TIMER_ABSTIME.
- rt_sigaction uses the k_sigaction layout for Linux-ABI processes: the old
action's restorer was written 112 bytes past the caller's struct. Flags
are kept; SIGKILL and SIGSTOP cannot be caught.
- F1..F12 reach programs, as the Linux console sends them (PS/2, USB, I2C).
- TIOCLINUX subcode 6 answers "no modifiers" instead of echoing the 6 back.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
- /dev/ptmx and /dev/pts/N: Unix98 pairs with a full line discipline,
window sizes, job control and hangup (kernel/dev/pty.c).
- The console speaks scroll regions, insert/delete line, SU/SD, RI/IND/NEL,
DECSC/DECRC; swallows charset designations and private CSI sequences;
and LF only returns the carriage under ONLCR.
- setsid() drops the controlling terminal, so a pane's pty becomes its ctty.
- pipe2() honours O_NONBLOCK and O_CLOEXEC (libevent's signal pipe).
- File modes are stored and enforced: chmod, fchmod(at), umask, creation
modes; /tmp is 1777.
- /proc/stat has real user/system/idle; /proc/<pid>/task; kthread flag.
- SO_PEERCRED, IOV_MAX 1024.
- /proc/strace: name a program and its syscalls go to the kernel log.
- World gains htop, btop, tmux, mc, ncdu, fastfetch, games, X toys, NetSurf.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
A panic no longer ends in a picture. The report is drawn as before, and
then GMMOS runs under it: the real kernel stays dead -- the other
processors are halted, and nothing of it is called that locks, sleeps,
allocates or waits for an interrupt -- and GMMOS keeps its own clock
(the TSC), its own keyboard (micro drivers, polled), and the screen.
On the report: a live status line counting down the three-minute
power-off, which any key cancels, and the keys.
Space the last 300 lines of this boot's log as QR codes, a page per
symbol, numbered; + and - trade module size for capacity
L the log on screen, scrolled
T a terminal: why, log, grep, ps, cpus, pci, mem (page tables
walked first, so a bad address cannot fault), uptime, restart,
poweroff
R R restart; P P power off -- twice, so a stray key does neither
The first micro driver is PS/2, polled: kbd.c with everything but the
keys taken out. The probe asks the keyboard to echo, so a controller
with nothing behind it is not offered as one. Polling also sidesteps the
IRQ 1 polarity quirk, which is about interrupt routing.
A panic inside GMMOS (or a second one in the report) is reported and
then only blinks; it does not re-enter GMMOS.
Checked under QEMU: every screen; two QR pages read off a screenshot
with zbar decode to the log text exactly; restart reboots; left alone it
still powers off at three minutes.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
A panic used to stop only the processor it happened on. The rest carried
on with a dead kernel: on the ASUS laptop the report flashed up and was
drawn over, and the fans stayed loud until the power button was held.
Now the panicking processor sends every other one an NMI, which arrives
even with interrupts off, and trap() halts a processor that takes one
while panic_stop is set -- first thing, before the canary check, since
that stack may be what broke. NMI gets its own per-CPU stack (IST 1):
for a few instructions at the top of syscall_entry the live stack is the
user's, at ring 0, and a fault pushing the frame there would be a double
fault on the same stack and a reset instead of a report.
A second processor that panics while one is already reporting halts
instead of drawing over it; the owner's own nested panic still gets
through.
Checked under QEMU with -smp 4: after a sysrq crash CPUs 1-3 sit in hlt
with IF clear and CPU 0 is in the report's blink loop.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
busybox wget hands TLS to ssl_client over a socketpair and then does
shutdown(SHUT_WR). That cut the AF_UNIX link both ways, so ssl_client's
reply was a SIGPIPE and every https:// download hung. SHUT_WR is now a
half-close: the peer reads EOF and can still answer. TCP sockets get
shutdown() at all (tcp_shutdown for the FIN); it used to do nothing.
- exec keeps ignored signals and the signal mask, as execve(2) says.
- /proc/<pid>/fd: a link per descriptor -- the path it was opened by,
socket:[n], pipe:[n], anon_inode:[eventpoll]. /proc/self too. The
global inode bit moves above pid << 8; at 0x10000 it was /proc/256.
- fstat on a socket or pipe answers S_IFSOCK / S_IFIFO instead of EINVAL.
- poll, select and epoll wake as soon as a pipe, socket or input device
changes, not on the next tick.
- Pipes are 64 KB of lazily allocated pages, copied in blocks, with
PIPE_BUF atomicity: 300 MB through `yes | head | wc` in 7 s.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
alarm() and setitimer() stored a countdown nothing counted down, so no
timer has ever fired; setitimer and getitimer were also registered with
no Linux number. alarmd now posts SIGALRM on the tick, while any process
has a timer armed. busybox's ping, /bin/ping on the Alpine root, sends
every request after the first from its SIGALRM handler.
It also opens SOCK_RAW, which was EPROTOTYPE. A raw ICMP socket is now a
ping socket whose reads start at the IP header. And a blocked socket
call gives up for a signal with a handler, not only for a kill: the
alarm woke recvfrom, and the wait put it straight back to sleep.
For Xorg: AF_UNIX abstract names, which read as the empty path and so as
EADDRINUSE ("server already running"); and getsockname and getpeername,
which did not exist, so libxcb sent no cookie and the server refused
every client.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
The live root was a fixed 96 MB image in the kernel: 60 MB of zeros on
the ISO, twice, and room for 60 MB of packages whatever the machine had.
Now the image is only what the root holds, plus slack, measured by
building it once large. Past its end the ramdisk goes on to half of the
memory free at mount, as pages taken the first time each block is
written; an unwritten block reads as zeros and costs nothing. SchFS
keeps no free-space map on disk, so growing a volume is a larger total
before open builds the map: grow_to, set for the ramdisk root.
8 GB machine: a 4 GB root, Xorg installed into it in 77 s with 7.6 GB
still free. The ISO is 172 MB instead of 344.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
Found by running Alpine's apk on SchOS, one failure at a time:
- chroot(2) was a stub returning EPERM. Each process now has a root:
where an absolute path starts and where .. stops. Mounts remember
whose root they were made under, and a walk leaves a mount by the way
it came in, so one filesystem can be mounted twice.
- devtmpfs and proc mounted only on /dev and /proc, whatever the target;
a chroot got "already mounted".
- mmap never reused freed address space, so musl's malloc used up the
256 mapping records while 780 MB were free. A mergeable mapping now
goes straight after an anonymous one whose end has room.
- unlinkat returned -1 (EPERM) where apk expects ENOENT, and renameat
was an old copy of rename: no replacing the target, and v1 dirents
written into SchFS. Both now share rename's implementation.
- execve runs #! scripts, and says ENOEXEC for what it cannot run.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
There were none: fcntl answered F_SETLK with EINVAL and flock was not a
system call. Alpine's apk, which runs unmodified on SchOS through
Alpine's own musl, locks its database before reading it and stopped
there.
kernel/fs/lock.c keeps one table of advisory locks keyed by (dev, inum):
flock() for the whole file, owned by the open file description;
F_SETLK/F_SETLKW/F_GETLK for byte ranges, owned by the process and
released when it closes any descriptor on the file or exits; and the
F_OFD_* forms, ranges owned by the description. flock and record locks
do not see each other, as on Linux. Waiters sleep until any release and
are interrupted by a signal.
cmd/locktest checks each between a parent and a child, including range
splitting, F_GETLK's report, and a blocked waiter being woken.
shell.nix gains pkg-config, meson, ninja, m4, bison, flex and xz, for
the X ports.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
An ASUS TUF A15 booted with its internal keyboard dead and a USB one
fine. These AMD laptops' firmware describes IRQ 1's polarity wrongly --
Linux keeps a quirk list -- and an edge line programmed the wrong way
up never fires: the controller holds its byte, and only the interrupt
that never comes would read it.
irq_watch() lets a driver say how to ask its device whether something
is waiting. The poller asks every tick; 50 ms of waiting with nothing
delivered turns the line's polarity over and drains the device, which
re-arms the edge, and if it still says nothing the line is polled.
Both are announced. The keyboard and the PS/2 mouse are watched.
ISA lines now also take their mode from the MADT's override entries,
which were parsed and never read.
Tested in QEMU, which ignores polarity on edge lines, with the keyboard
line masked: the first key turns it over and typing works; masked again
after the flip, it is polled and typing still works.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
The set libwayland's event loop is made of, in kernel/sys/sys_event.c:
four kinds of descriptor with no inode, FD_EVENT, that read() drains
and poll() reports on. They were table entries returning ENOSYS that
read as done.
epoll registers (descriptor, file) pairs, so a closed descriptor
leaves the set; level- and edge-triggered, EPOLLONESHOT. Waiting is
poll()'s, a tick at a time. The old eventfd and signalfd numbers (284,
282) were aliased to the new calls and read flags from a garbage
register; they are their own entries now, with epoll_create and
epoll_pwait.
cmd/evtest checks each, then all four in one set. The plans are
brought up to date: everything Wayland was waiting on is built except
setsockopt.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
sigsend() ended a process for a default-fatal signal (SIGUSR1, SIGTERM,
SIGINT...) on arrival, whatever its signal mask said. Blocking is
exactly the promise that it will not: the signal waits until it is
unblocked, or until the program takes it some other way -- which is
what signalfd is, and how this was found.
A blocked signal is now only made pending. If it is later unblocked
while still pending, deliver_signals() applies the default action
then. SIGKILL cannot be blocked, as before.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
- schinit, schinitd and vgpud build every message from pieces, one
write() each, so a job starting on another CPU landed mid-line:
"schinitd: starting vgpud: os.schos.resolvconfno virtio-gpu on this
machine". They now collect a line and write it at the newline;
resolvconf's verbose line is one write with its prefix.
- The ACPI SCI registers IRQ_QUIET. A desktop's SCI never fires, and the
poller took two seconds of silence for a misrouted line ("irq 9:
nothing has arrived on it") and called the handler every tick. A line
is only exempt while every handler on it is quiet.
- The loader claims each segment from where the last one's claim ended,
so two segments sharing a page no longer ask for it twice. When a
claim is still refused, it names the memory-map entries in the way.
- Stale divesymlink() declaration gone; the kernel.md struct table
re-measured (inode, buf and file pools grow from slabs now).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
Sixty-five headers sat side by side in include/, so `#include "irq.h"`
said nothing about where irq.h was or what it belonged to, and errno.h,
stat.h and fcntl.h at the top shadowed the system's for any host tool
built with -I./include. They are in folders now -- arch/ core/ fs/
dev/ gfx/ net/ uapi/ (and ldls/ for the Linux driver layer) -- and
every include names the folder, as Linux's do: "core/proc.h".
Done mechanically and checked the hard way: the kernel built from this
tree disassembles identically to the one built from the tree before
it. The full image boots, and userland is the same set of programs.
Paths in docs and comments follow; docs/guides/layout.md has a table
of what is where, and tools/fix-includes.py rewrites old-style
includes from the folders in the tree, for code written before this.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
